The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A camshaft actuates valves of an internal combustion engine. In a dual overhead camshaft configuration, the engine includes an exhaust camshaft and an intake camshaft for each bank of cylinders. Rotation of the camshafts actuates intake and exhaust valves of the engine. Position and timing between a crankshaft and the camshafts are adjusted for proper synchronization of spark ignition and fuel injection, which improves engine efficiency in fuel consumption and pollutant exhaustion.
An engine control system may include one or more camshaft phasing devices (cam phasors). A cam phasor may be used to create a continuously variable rotational offset between the exhaust camshaft and the intake camshaft and/or the crankshaft, which alters opening and closing time between intake and exhaust valves. Typically, cam phasors receive position information from a camshaft position sensor. The camshaft position sensor sends a signal to a control module. The control module develops an offset signal with respect to a commanded position signal, to control the cam phasors.
A cam phasor based control system typically includes a hydraulic actuator and control valve. The control valve is used to adjust passage of hydraulic fluid to the hydraulic actuator based on a position command signal and a current camshaft position signal. Viscosity and pressure of the hydraulic fluid can vary, which affects dynamic control performance. Cam phasor based control systems tend to be sensitive to variations in engine oil temperature, age and pressure, as well as noise due to position sensor variations. The control systems also tend to have varying response times. This can negatively affect engine performance.